In an optical device such as a semiconductor laser module, in order to enhance an optical coupling rate between a functional part (such as an LD chip) of the optical device and a core of an optical fiber, it is necessary to highly precisely align the functional part and the core of the optical fiber with each other and maintain the positional relationship between the functional element and the core of the optical fiber. If such a positional relationship is destroyed (misalignment is caused), the optical device cannot demonstrate desired characteristics, resulting in a defective product.
FIG. 1 is a front view schematically showing a conventional optical fiber fixation structure. As shown in FIG. 1, in the conventional optical fiber fixation structure, a fiber mount 140 is fixed to an upper surface 111A of a base plate 111, and a resin 150 is applied as an adhesive agent to an upper surface 141 of the fiber mount 140. Thus, the optical fiber 130 is fixed to the fiber mount 140 by the resin 150.
However, in the conventional optical fiber fixation structure, the resin 150 may come off the fiber mount 140, for example, when a strong tensile stress is applied to the optical fiber 130. If the resin 150 comes off the fiber mount 140, the optical fiber 130 moves freely on the fiber mount 140 so that the optical fiber 130 is deviated from the semiconductor laser device 122 (positional misalignment is caused). Thus, in the conventional optical fiber fixation structure, the resin 150 that comes off directly causes positional misalignment of the optical fiber 130. Therefore, the conventional optical fiber fixation structure problematically has low reliability.
In order to prevent such positional misalignment of an optical fiber, there has been proposed a method of using a fiber fixing pedestal in which a groove is formed along an optical axis of an optical fiber and fixing the optical fiber to the fiber fixing pedestal by an adhesive agent (see, e.g., Patent Literature 1). With this method, the adhesive agent is disposed within the groove formed in the fiber fixing pedestal so as to form spaces above and below the optical fiber. Those spaces provide relief for the shape change of the adhesive agent upon expansion or shrinkage of the adhesive agent. Therefore, an excessive force is prevented from being applied to an outer circumference of the optical fiber.
In such a method, however, a groove needs to be formed along an optical axis of an optical fiber in the fiber fixing pedestal. Therefore, a structure for fixing the optical fiber becomes complicated, and the cost for manufacturing such a structure also increases. Furthermore, in order to reduce the positional misalignment of the optical fiber due to thermal shrinkage or expansion of the adhesive agent, which is caused by various factors including shrinkage of the adhesive agent upon curing for fixing the optical fiber, the location and angle of the groove of the fiber fixing pedestal needs to match accurately with the optical axis of a laser beam emitted from the semiconductor laser device. Therefore, it is feared that the manufacturing process of the semiconductor laser module becomes cumbersome.
Moreover, since the groove of the fiber fixing pedestal extends along the optical axis of the optical fiber, the adhesive agent may come off the fiber fixing pedestal if a tensile stress is applied along the optical axis of the optical fiber. Accordingly, the positional misalignment of the optical fiber is likely to occur as with the structure shown in FIG. 1.